Utilizating the human X-linked enzymes glucose-6-phosphate dehydrogenase (G6PD) and hypoxanthine-guanine phosphoribosyl transferase (HGPRT), and the autosomal enzyme lactic acid dehydrogenase (LDH) we plan to continue studying: (a) The relationship between X-chromosome regulation and somatic development in ante and postnatal males and females with sex chromosomal imbalance states. (b) The difference in sensitivity to 8-azahypoxanthine between cultured normal and malignant human cells. (c) The biochemical genetics of malignant hybridization in order to locate genetic loci responsible for malignant transformation as well as antimalignant loci too. We plan to use isolated intact metaphase chromosomes to accomplish malignant transformation of cultured normal diploid fibroblasts rather than hybridization with intact living malignant cells as has been the procedure in other studies.